1. Field of the Invention
The present invention relates to exposure apparatus, exposure methods, and device manufacturing methods, and more particularly, to an exposure apparatus and an exposure method used in a lithographic process for manufacturing electronic devices such as a semiconductor device as in an LSI, a liquid crystal display device, a pick-up device as in a CCD, or a thin-film magnetic head, when transferring a pattern formed on a mask or a reticle (hereinafter generally referred to as a “reticle”) onto a substrate such as a wafer, and a device manufacturing method using the exposure apparatus and exposure method.
2. Description of the Related Art
Circuit patterns are becoming finer according to higher integration in devices such as semiconductors, and in order to cope with such a situation, requirements for an improvement in the resolution of exposure apparatus are pressing, which requires exposure wavelength in a shorter range. Recently, as a successor to the exposure apparatus using the KrF excimer laser (output wavelength: 248 nm) as its light source, an exposure apparatus that uses an Argon Fluoride excimer laser (ArF excimer laser) having an output wavelength of 193 nm as its light source has been put to practical use. With the exposure apparatus using the ArF excimer laser as its light source, electronic devices (micro devices) that have fine patterns with the practical minimum line width (device rule) from 0.18 μm up to 0.10 μm can be mass-produced.
In an exposure apparatus, other than resolution, overlay accuracy of a reticle pattern on a pattern already formed on a shot area is also significant. In order to maintain favorable overlay accuracy, aberration has to be suppressed in the projection optical system used as much as possible. To control the aberration, conventionally, a measurement technique was employed that performed the following operations: exposing a predetermined measurement pattern on a reticle onto a substrate via a projection optical system, developing the substrate, measuring line width, positional deviation, and the like of a resist image formed on the substrate using equipment such as a scanning electron microscope (SEM), and obtaining the aberration of the optical system based on the measurement results.
However, when it comes to measuring fine patterns of 0.13 μm and under, the measurement technique having the process of using equipment such as the above SEM has its limits. This is because of reasons such as: errors may occur in reticle manufacturing such as fabricating errors of measurement patterns, errors may be caused in the process of resist coating and development of the substrate, or errors and deterioration of measurement reproducibility may occur when equipment such as the SEM is used. Therefore, recently, the trend is moving toward securing the performance of the projection optical by wavefront aberration. Since measurement by wavefront aberration does not require any process in between, performance of the projection optical system can be guaranteed at a higher precision.
Such methods of securing the performance of the projection optical system by wavefront aberration include a method of measuring the wavefront aberration of the projection optical system using an exclusive wavefront measurement unit that uses interferometers or the like in the adjustment process of the projection optical system itself, and adjusting the aberration precisely, based on the measurement results. In this method, however, when the environment changes in between a state where the projection optical system stands alone and a state where the projection optical system has been incorporated into the main body of the exposure apparatus, or when an accident occurs during the incorporation into the main body of the exposure apparatus, quality assurance on shipment is insufficient, and in some cases, not possible. For such reasons, mainly from the viewpoint of quality assurance, which is performed by measuring the wavefront aberration right before shipment and adjusting the aberration of the projection optical system based on the measurement results, proposals are recently made on a wavefront measurement unit that can measure the wavefront aberration even after when the projection optical system is built into the exposure apparatus, such as a compact wavefront measurement unit (wavefront measurement instrument), which can be provided inside the exposure apparatus by attaching it to the substrate stage or exchanging it with the substrate stage.
However, as is described so far, since the main purpose of the above conventional wavefront measurement instrument was to measure the wavefront aberration of the projection optical system from the viewpoint of quality assurance on shipment, the above conventional wavefront measurement instrument was not designed for measurement of the wavefront aberration of the projection optical system after shipment. Therefore, the wavefront measurement instrument was not attached to the exposure apparatus after shipment, and the exposure apparatus itself did not have a suitable configuration to perform wavefront measurement frequently. This caused difficulty in performing sufficient quality control on the projection optical system during normal usage of the exposure apparatus.